In the oil industry, slips have been essential components of oil field drilling and servicing equipment for many years. Conventional manual slips are sets of heavy hinged blocks with gripping dies that are positioned in a slip bowl of a rotary table to engage a drill pipe, casing or production tubing. Angled surfaces in each slip block mate with complementary surfaces in the slip bowl. The complementary surfaces cause axial forces exerted by the weight of the pipe on the gripping dies to be transferred into lateral gripping pressure on the pipe, which supports the pipe and thus prevents it from dropping into the well when a free end of the pipe is released for any reason.
As is well known in the art, conventional slips are often manually engaged by oil field personnel who physically maneuver the slips into the slip bowl so that they slide into engagement with the casing or drill pipe. The slips are disengaged by upward axial movement of the casing, drill pipe, or production tubing to take the weight off the slips. The slips are then lifted out of the slip bowl. An example of such conventional slips is described in U.S. Pat. No. 4,244,093, which is entitled TUBING SLIP PULLING TOOL and issued to Klingensmith on Jan. 13, 1981.
There is an ever-increasing demand for obtaining more oil and gas from existing wells. After a primary recovery term of a well has elapsed, some form of reworking is required to remove residual oil and/or gas from the well. Usually in reworking those wells, such as in preparation for a well stimulation process, the tubing string must be removed from the well or pulled up for attachment of wellhead tools, and then lowered again to insert the wellhead tools through the wellhead. During such operations, the tubing string is typically secured by slips. It is therefore necessary to remove and set the slips in preparation for a well stimulation process. Consequently, slips are not only frequently used during well drilling and completion; they are also required equipment for well re-completion, servicing and workover.
However, manual handling of slips can be dangerous and time-consuming. Accordingly, hydraulically powered equipment has been introduced for positioning slips. An example of a hydraulically operated slip assembly used to grip pipe as it is being run into or pulled from a well is described in U.S. Pat. No. 5,027,926 entitled SLIP ASSEMBLY, which issued to Cox on Jul. 2, 1991. However, Cox does not provide any pressure containment.
There is therefore a need for a slip spool that facilitates the setting and resetting of a tubing string in a live well bore.